Answer: 515.35 J
Explanation:
x: m1 x v1=(m1+m2) x v(x)

y: m2 x v2 =(m1+m2) x v(y)

v(x)= m1 x v1/(m1+m2) =75x4/(75+91)= 1.81 m/s

v(y) =m2 x v2 /(m1+m2)= 91 x 3 /(75+91)= 1.64 m/s

v=sqrt[v(x)^2 +v(y)^2] = 2.44 m/s

φ =arctan {v(y)/v(x)} = 47.82 degrees 

∆K = Kf −Ki =(m1 x v^2/2 +m2 x v^2/2) - (m1 +m2) x v^2/2 =

=(75 x 16/2 +91 x 9/2) –(75+91) x 2.44^2/2
= (600 + 409.5 ) - (166 x 2.98) = 515.35 J
